1. Technical Field
The present invention relates in general to an improved disk drive, and in particular to an improved means of identifying the planar orientation and rotational position of disks in a disk drive.
2. Description of the Related Art
Generally, a data access and storage system consists of one or more storage devices that store data on magnetic or optical storage media. For example, a magnetic storage device is known as a direct access storage device (DASD) or a hard disk drive (HDD) and includes one or more disks and a disk controller to manage local operations concerning the disks. Typically, one or more disks are stacked vertically on a common spindle that is turned by a disk drive motor at several thousand revolutions per minute (rpm).
Disks are rigid platters that are usually made of aluminum alloy, plastic, glass, or ceramic, and are covered with a magnetic coating on each side or surface (i.e., xe2x80x9cA-sidexe2x80x9d and xe2x80x9cB-sidexe2x80x9d). During the fabrication of the platters, grippers (at least three, but usually four) are used to grip each platter along its outer circumferential edge. The grippers are symmetrically spaced apart from each other around the perimeter of the platter as the various manufacturing processes, such as sputtering, are performed on the platter. When the grippers release the platter after sputtering, tool marks or xe2x80x9cshadowsxe2x80x9d along the disk outer edge where the sputtering was prevented from contacting the disk are present.
The only other moving part within a typical HDD is the head stack assembly. Within most HDDs, one magnetic read/write head or slider is associated with each side of each platter and flies just above or below the platter""s surface. Each read/write head is mounted on a suspension to form a head gimbal assembly (HGA). The HGA is then attached to a semi-rigid arm apparatus that supports the entire head flying unit. Several semi-rigid arms may be combined to form a single armature unit.
Each read/write head scans the surface of a disk during a xe2x80x9creadxe2x80x9d or xe2x80x9cwritexe2x80x9d operation. The head and arm assembly is moved utilizing an actuator that is often a voice coil motor (VCM). The stator of a VCM is mounted to a base plate or casting on which the spindle is also mounted. The base casting is in turn mounted to a frame via a compliant suspension. When current is fed to the motor, the VCM develops force or torque that is substantially proportional to the applied current. The arm acceleration is therefore substantially proportional to the magnitude of the current. As the read/write head approaches a desired track, a reverse polarity signal is applied to the actuator, causing the signal to act as a brake, and ideally causing the read/write head to stop directly over the desired track.
In the prior art, each tool used in the disk manufacturing process has its own unique machine index for circumferentially referencing the disks. The machines indices are referenced from the A and B sides of each platter. Thus, when a disk is transferred, for example, from a manufacturing tool to a test tool, the two different tools utilize different machine indexes. Whatever circumferential disk reference the manufacturing tool utilized is lost when the disk is transferred to the test tool. This loss of information is repeated at each tool change. Moreover, information pertaining to only one of the A and B sides also may be lost if the disk is inverted. Thus, an improved means of identifying the rotational position and planar orientation of disks is needed.
One embodiment of a disk for a hard disk drive uses a circular platter having first and second sides and a circumferential edge. The circumferential edge of the disk has four symmetrically spaced apart shadows and a xe2x80x9cfifthxe2x80x9d or additional shadow, thereby giving the disk an asymmetrical shadow signature. The fifth shadow is offset relative to the other shadows, which have congruent arcuate lengths and separation. The fifth shadow has an arcuate length that is about half as long as those of the other shadows, and is closely spaced adjacent to one of the other shadows.
The asymmetric shadow signatures of the disk is used to precisely determine both the circumferential position of the platters and their planar orientation (i.e., A-side or B-side). For example, when the disk is mounted on a tool spindle and rotated, an optical detector detects the pattern of the shadows and feeds the data to a computer system. The rotational position of the spindle also is relayed to the computer for coordinating the processing of the rotating disk. When the disk is mounted on a different tool, the same shadow signature is used to determine its planar and angular positions.
The foregoing and other objects and advantages of the present invention will be apparent to those skilled in the art, in view of the following detailed description of the preferred embodiment of the present invention, taken in conjunction with the appended claims and the accompanying drawings.